1. Field of the Invention
The present invention relates to a semiconductor device and to a method for manufacturing semiconductor devices that reduces the size of semiconductor devices and improves the yield.
2. Prior Art
One type of semiconductor device assembly method is a tape carrier method. Essentially, in this assembly method, as seen from FIG. 7, numerous leads 76 consisting of a conductive layer are formed on the upper surface of a carrier film 2 that is made of a band-form heat-resistant resin film. Then, these leads 76 are bonded to bumps that are surface electrodes of semiconductor chips 78. In addition, these elements are sealed with a resin.
More specifically, in this tape carrier method, the tip ends of the leads 76 formed on the surface of the carrier film 2, as seen from FIG. 8, overhang from windows 2a of the carrier film 2, and the semiconductor chip 78 is caused to approach the leads 76 from below. Then, the leads 76 and bumps 80 are thermally fused while being heated and pressed from above by a bonding tool that has a heater, thus bonding the leads 76 and bumps 80. Bonding of the leads 76 and bumps 80 can be done by another way. A molten resin material in which a conductive powder is dispersed and held is applied to the interfacial surfaces of the leads 76 and bumps 80 and then hardened.
In recent years, a flip-chip method is also used. In this method, as seen from FIG. 9, leads 76 are formed on the surface of a carrier film 82, and semiconductor chips 78 that are set upside down are caused to approach the leads 76 from above, and bonding is performed on the leads and bumps.
However, even in this flip-chip method, there are problems. When achieving a finer pitch, it is likely that more defective products are produced, thus causing yield drop. A detailed investigation of such defective products done by the inventor found the causes of such defective bonding. When the lead 76 contacts a position that is away from the center of the corresponding bump 80, the application of pressure in this state causes the lead 76 to slip on the upper surface of the bump 80 as shown in FIG. 10. As a result, the deviation S increases, and the lead 76 falls from the upper surface of the bump 80.
Accordingly, the object of the present invention is to provide a semiconductor device that, in its manufacturing process, is able to prevent slipping between the leads and bumps, thus preventing falling of the leads from the bumps.
A further object of the present invention is to provide a manufacturing method of semiconductor devices that is able to realize a much greater reduction in the size of semiconductor devices and also realize an improvement in the yield.
The above object is accomplished by a unique structure for a semiconductor device in which bumps formed on the surface of a semiconductor chip and leads are set to face each other and bonded, wherein
a recess is formed in the surface of each one of the bumps that faces a lead,
the recess comprises guide-surfaces that are inclined surfaces and are formed between the bottom of the recess and the opening edges of the recess, and
each of the leads is provided with a projection at one end thereof, the projection being to be bonded to a bump and provided with guided-surfaces that are inclined surfaces.
In this structure, when the bump and the lead are faced and pressed each other, the lead is guided toward the center of the upper surface (or the bottom) of the bump by the guide-surfaces of the bump and by the guided-surfaces of the lead that are inclined. Accordingly, even when the lead contacts a position that is away from the center of the bump, the lead does not fall from the bump. Furthermore, since the lead is guided by the inclined surfaces, a stress acts toward the lead from the opening edges of the bump, and the lead is held firmly on the bump. Accordingly, an assured bonding is performed, reduced size semiconductor devices are produced, and it is possible to realize the improvement in the yield.
In the above structure, the inclined guide-surfaces are formed for the entire periphery of the recess of each bump. Also, the guided-surface are formed so as to be inclined for the entire periphery of each lead and so as to surround a bonding point (a point that is bonded to the corresponding bump) of the lead.
Accordingly, the lead is guided into the recess of the bump from any directions around the entire periphery of the lead.
Furthermore, in the above semiconductor device, the width of the end surface of the lead that faces the bump is set to be narrower than the width of the lead.
By way of designing the end surface of the lead that faces the bump so as to be narrower than the width of the lead, the lead is accurately guided into the recess of the bump. In addition, this structure provides the lead with a structural strength, the deformation thereof is thus prevented, and it is ideal for meeting a required finer pitch.
The above object is further accomplished by unique steps of the present invention for a method for manufacturing a semiconductor device in which bumps formed on the surface of a semiconductor chip and leads are set to face each other and bonded; and in the present invention, the method includes:
a step of forming a recess in the surface of each of the bumps that faces the lead, the recess having inclined surfaces between the bottom of the recess and the opening edges of the recess, and
a step of forming a projection at one end of each of the leads, the projection being to be bonded to each of the bumps and provided with guided-surfaces that are inclined surfaces.
In this method, each bump has guide-surfaces that are inclined surfaces and each lead has guided-surfaces that are inclined surfaces that mate the inclined surfaces of the bump. Accordingly, when the bump and the lead are faced and pressed each other, the lead is guided into the center of the upper surface (or the bottom) of the bump by the guide-surfaces of the bump and the guided-surfaces of the lead. Accordingly, even when the lead contacts a position that is away from the center of the bump, the lead does not fall from the upper surface of the bump. Furthermore, since the lead is guided by the inclined surfaces of the bump, a stress acts toward the lead from the opening edges of the bump, and the lead is held firmly on the bump. Thus, bonding is performed securely, reduced size semiconductor devices can be produced, and it is possible to realize the improvement in the yield.
In the above method, the inclined guide-surfaces are formed around the entire periphery of the recess of each bump, and the guided-surfaces are formed around the entire periphery of the bonding point (a point that is bonded to the corresponding bump) of each lead. Thus, the lead is guided into the recess of the bump from any directions around the entire periphery of the lead.
Furthermore, in the above method, the width of the end surface of a lead that faces a bump is formed so as to be narrower than the width of the lead. Since the end surface of the lead that faces the bump is narrower than the width of the lead, the lead is accurately guided into the recess of the bump. In addition, the lead has a structural strength, the deformation thereof is prevented, and it is ideal for manufacturing finer pitch semiconductor devices.